1. Field of the Invention
The present invention relates to a pressure wave charger for the charging of internal combustion engines, with a cell rotor, one side of which is closed off by a gas housing and the other by an air housing. The air housing comprises a bearing device for the rotor shaft of the cell rotor.
2. Description of Related Art
For pressure wave chargers used as supercharging assemblies for vehicles with internal combustion engines there exists a general problem in integrating the cell rotor into the other components of the pressure wave charger, particularly with respect to the operation of the bearings. As shown herein, special attention must be paid to the bearing layout.
From EP-0 087 834 B1 a bearing for the cell rotor is known, which is capable of eliminating the disadvantages of the earlier solution wherein the cell rotor was bearingly supported in slide bearings supplied with oil by the lubricating oil system of the engine. This embodiment had the risk that in case of an interruption in the oil supply, for example by the rupture of an oil line, the rotor could be destroyed very rapidly as the result of its high speed of rotation. The bearing of the cell rotor provided by the aforecited reference includes measures assuring a metered, continuous supply of lubricants by means of the introduction of grease from a grease reservoir into the bearings.
In the reference, the rotor shaft is located in the air housing of the pressure wave charger, with the cell rotor fastened by means of its hub to the inner end of the rotor shaft. In this axial fastening mode, the stop face of the cell rotor is mostly located outside the bearing symmetry of the rotor shaft.
If the aforedescribed bearing support of the proportional drive of the pressure wave charger is replaced by a free running pressure wave charger driven by the forces of the gases of the internal combustion engine, such as known for example from European patent application No. 87 101 608.5 of the present applicant, the bearing layout created in this manner would not be optimally correct because of the slight difference between the high operating speed and the critical speed of the bearing layout.
In addition, the installation of cell rotors consisting of a ceramic material, such as those described in EP 0 051 327 B1, could not be recommended, in view of the continuing absence of bearing devices suitable for ceramics.
Based on a bearing device according to the above state of the art, a free running pressure wave charger and a ceramic cell rotor, would lead to a series of inadequacies:
The closeness of the operating speed to the critical bending speed in the case of the first-mentioned bearing layout often leads to vibrations because of the difference between the gravity centers of the mass of the cell rotor and the bearing symmetry.
The static undeterminancy of the rotor shaft support results in stresses in the bearings integrated into the air housing, with negative effects on the running properties of the cell rotor coupled with the rotor shaft.
The rotor shaft rotatably supported in the air housing limits the flow cross section excessively because of the prevailing hub ratio, i.e., its inlet and outlet channel on the air housing side.
The product of the average bearing diameter and its speed is limited in the case of grease lubrication; for this reason the average diameter must be kept small at a given speed.
The mounting of a free running cell rotor on the rotor shaft by means of a necessarily small shoulder as the parallel stop, easily leads to a tilting of cell rotors relative to the axis of the rotor shaft. The result is a wobbling of the rotor while running. Any mounting of the cell rotor on the rotor shaft would lead, in the case of the installation of a ceramic cell rotor, to interference with its seating as the result of the operationally dependent different thermal expansions between the ceramic cell rotor and the metal rotor shaft, even if the hub of the cell rotor is made of an aluminum alloy.
The transfer of heat from the cell rotor to the bearings and the rotor shaft may be impeded by expensive measures only.